The present invention relates to a scroll-type apparatus for use in a pump, a compressor, or an expander. In particular, it relates to a scroll-type apparatus having adjustable seal means for achieving an effective contacting or non-contacting radial seal of a desired size.
Rotating apparatuses of the scroll type have been known from long in the past. An early such apparatus was disclosed in U.S. Pat. No. 801,182 issued to Leon Creux in 1905. The apparatus disclosed therein was in the form of a rotary engine operated by an elastic fluid. The principles on which this engine are based have been applied to a large variety of machines, including compressors, pumps, and expanders in addition to engines.
In general, a scroll-type apparatus comprises two interfitting scrolls comprising parallel spiroidal or involute spiral wraps of the same shape which are mounted on separate parallel base plates. One of the spiral wraps is caused to rotate about the center of the second spiral wrap. The two spiral wraps touch one another at a certain number of points so as to form between the spiral wraps and base plates a plurality of compression chambers which change in size as the first spiral wrap is rotated. A compressible fluid introduced from the side of one of the spiral wraps is compressed as it is moved towards the center of the spiral wraps and then is then discharged from the center of the spiral wraps. By varying the direction of rotation, the apparatus can produce either expansion or compression of the compressible fluid.
While this type of apparatus has a number of advantages, it has significant problems related to wear and sealing. Due to the complicated non-linear motion of the parts, it is difficult to obtain effective radial and tangential seals. If such an apparatus is to operate efficiently, effect axial contact must be realized between the ends of the involute spiral wraps and the base plate surfaces which they contact to seal against radial leakage. Furthermore, effective radial contact must be attained between the pairs of spiral wraps where they contact one another.
One means which has been used in the past of achieving radial sealing is to machine the wraps and base plates to highly accurate shapes so that there is only a very small gap left between the ends of the spiral wraps and the opposing base plates, and these gaps are sealed by an oil film formed by oil entrained with the fluid being compressed. However, this method is disadvantageous in that the machining is extremely costly, and it is impossible to achieve clearances which allow effective sealing at all times during operation. Namely, a gap which is of the appropriate size for use when the apparatus is cool will be too small once the scrolls become heated during operating and thermal expansion of the spiral wraps closes the gaps, resulting in seizing. On the other hand, if the initial dimensions are such that an effective seal will be maintained after thermal expansion has occurred, then the gap will be too large when the apparatus is cool, and effective sealing will not be maintained. Furthermore, as the amount of thermal expansion is not uniform throughout the apparatus, the machining process becomes even more complicated.
U.S. Pat. No. 3,994,636 discloses a scroll-type apparatus in which a radial seal is achieved by seal elements associated with involute wraps which are urged by an axial force to make sealing contact with the base plates of the opposing scroll members. Spiral-shaped seal members are placed in grooves formed in the top of the spiral wraps. The grooves are wider than the seal members so that pressurized fluid can enter the bottom of the grooves and press the seal members against the base plate of the opposing scroll and achieve a contacting seal.
Since the seal members do not completely fill the grooves, it is possible for pressurized fluid to flow along the grooves in the spiral direction from an area of high pressure to one of low pressure, i.e. from one compression chamber to another. Accordingly, even though the seal members can provide a seal in the radial direction of the scrolls, the seal in the tangential direction is not fully satisfactory.
Furthermore, since the seal members are forced against the opposing base plates, frictional resistance decreases the efficiency of the apparatus and produces wear of both the seal members and the base plates.
Japanese Patent Publication No. 56-28240 also discloses a scroll apparatus in which seal members provided in grooves in the end surfaces of the spiral wraps are forced against the opposing base plates by pneumatic face force. That invention has the same drawbacks as the above in that it is possible for pressurized fluid to leak in the tangential direction from an area of high pressure to low pressure, and the contact between the seal members and the base plates produces wear and reduces efficiency.